Combination circuit breaker-lightning arrestor

Abstract

A conventional automatic electric circuit breaker is combined with a varistor to provide both overcurrent and overvoltage circuit protection. The varistor is connected between the load end of the circuit breaker and neutral to shunt to ground the currents associated with lightning induced voltage surges. As a fail-safe feature, abnormal leakage current drawn by the varistor under normal line voltage conditions directly and/or indirectly heats the thermal element of the breaker trip unit, ultimately tripping the breaker.

Having described my invention, what I claim as new and desire to secure by Letters Patent is: 
     
       1. A fail-safe lightning arrestor comprising, in combination: A. a circuit breaker including (1) a molded case compatible for installation in a circuit breaker panelboard,   (2) a line terminal for electrical connection to an electrical service entry main feeding the panelboard,   (3) circuit interrupting contacts, and   (4) an automatic trip mechanism including a thermally responsive trip element mechanically operative to initiate tripping of said contacts to an open circuit condition; and     B. a lightning induced voltage surge suppressor capable of dissipating at least 20 joules of energy, said suppressor including (1) a first terminal connected to said line terminal through said contacts, and   (2) a second terminal for connection to an electrical ground,   (3) said suppressor providing a continuous circuit path between its terminals and being operative, with said contacts closed, to shunt to ground the currents associated with lightning induced voltage surges appearing on the service entry main, and   (4) said suppressor accommodated in said molded case in thermally coupled relation with said trip element such that heat generated by said suppressor in response to abnormal current drawn by said suppressor under normal voltage conditions eventually leads to trip initiating mechanical operation of said trip element.     
     
     
       2. The fail-safe lightning arrestor defined in claim 1, wherein said voltage surge suppressor consists exclusively of a metal oxide varistor. 
     
     
       3. The fail-safe lightning arrestor defined in claim 1, wherein said line terminal is in the form of a female stab connector capable of plug-on electrical engagement with a male stab connector in a service entry panelboard and to which the service entry main is electrically connected. 
     
     
       4. The fail-safe lightning arrestor defined in claim 3, which further includes an electrical lead having one end connected to said second terminal of said voltage surge suppressor internally of the case and extending externally of said case through a portal therein to facilitate electrical connection of its other end to electrical ground. 
     
     
       5. The fail-safe lightning arrestor defined in claim 4, wherein said voltage surge suppressor is comprised exclusively of a metal oxide varistor. 
     
     
       6. The fail-safe lightning arrestor defined in claim 1, wherein said trip mechanism further includes magnetic trip elements mechanically operative to trip said contacts to their open circuit condition in response to high level abnormal current drawn by said suppressor. 
     
     
       7. A fail-safe lightning arrestor comprising, in combination: A. an automatic electric circuit breaker including (1) a line terminal for connection to an electrical service entry main,   (2) a load terminal for connection to an external branch load circuit,   (3) circuit interrupting contacts, and   (4) a thermal-magnetic trip unit including a. a bimetal electrically connected in series circuit with said contacts between said line and load terminals, said bimetal mechanically operative upon being directly heated by current of overload proportions drawn by the external load circuit to initiate tripping of said contacts to their open circuit condition, and   b. electromagnetic trip elements magnetically coupled with said series circuit and mechanically operative to initiate tripping of contacts to their open circuit condition in response to current of heavy overload and short circuit proportions drawn by the external load circuit; and       B. a varistor having a first terminal connected to said series circuit at a point downstream from said contacts and said electromagnetic trip elements, said varistor being in thermally coupled relation with said bimetal.   C. whereby, the heat generated by said varistor in response to low level abnormal current flowing therethrough under normal voltage conditions eventually precipitates trip initiating mechanical operation of said bimetal, while current of heavy overload and short circuit proportions drawn by said varistor under normal voltage conditions precipitates trip initiating mechanical operation of said electromagnetic trip elements.   
     
     
       8. The fail-safe lightning arrestor defined in claim 7, which further includes a molded circuit breaker case mounting said line and load terminals in externally accessible relation, said case housing said breaker contacts and trip unit, and said varistor in thermally coupled relation with said bimetal. 
     
     
       9. The fail-safe lightning arrestor defined in claim 8, wherein said first terminal of said varistor is electrically connected internally of said case to said breaker series circuit at a point intermediate said bimetal and said load terminal. 
     
     
       10. The fail-safe lightning arrestor defined in claim 9, wherein said molded case is acceptable in a conventional circuit breaker mounting position within a circuit breaker service entry panelboard, and said line terminal is in the form of a female stab connector capable of plug-on electrical engagement with a panelboard male stab electrically connected to a service entry main, said fail-safe ligntning arrestor further including an electrical lead wire connected at one end to said varistor second terminal within said case and extending externally of said case through a portal therein for the electrical connection of its other end to a grounded panelboard neutral bus. 
     
     
       11. The fail-safe lightning arrestor defined in claim 10, wherein said varistor is a metal oxide varistor. 
     
     
       12. Fail-safe lightning arrestor apparatus for installation in a circuit breaker panelboard fed from a single-phase, three-wire service entry having two mains and a neutral, the panelboard including a grounded bus to which the service entry neutral is connected, a pair of main bus bars to which the two service entry mains are individually connected, and a plurality of aligned male stabs alternately connected to the two main bus bars, each male stab being physically associated with a different breaker mounting position within the panelboard, said lightning arrestor apparatus comprising, in combination: A. a pair of combination circuit breaker-lightning arrestors, each including (1) a molded case compatible for mounting in a circuit breaker mounting position within a panelboard,   (2) an automatic electric circuit breaker accommodated within said case, said circuit breaker including a. a line terminal in the form of an externally accessible female stab connector mounted by said case,   b. an externally accessible load terminal mounted by said case,   c. circuit interrupting contacts accommodated within said case, and   d. a trip unit accommodated within said case and including a thermally actuated trip element connected in series circuit with said contacts between said line and load terminals, said trip unit being automatically operable to precipitate opening of said contacts to interrupt said series circuit, and     (3) a voltage surge suppressor accommodated within said case in thermally coupled relation with said trip element and having a. a first terminal connected to said series circuit at a point beyond said contacts and said trip element from said line terminal,   b. a second terminal, and   c. a lead wire electrically connected at one end to said second terminal internally of said case and extending externally of said case through a portal therein to facilitate electrical connection of its other end to the grounded panelboard neutral bus; and       B. means joining said cases of said combination circuit breaker-lightning arrestor pair in side-by-side relation;   C. whereby said lightning arrestor apparatus is installable in adjacent circuit breaker mounting positions within the panelboard with the line terminal female stab connectors of said combination circuit breaker lightning arrestors plugged on the panelboard male stabs associated with the adjacent breaker mounting positions, said voltage surge suppressors being thereby individually connected in circuit across a different one of the service entry mains and the service entry neutral to shunt to ground the currents associated with lightning induced voltage surges appearing on either of the service entry mains, and the heat generated by either of said suppressors in response to abnormal current flowing therethrough under normal line voltage conditions is coupled to said trip element of the associated circuit breaker, ultimately leading to automatic operation of said trip unit to precipitate opening of said contacts of said associated circuit breaker.   
     
     
       13. The fail-safe lightning arrestor apparatus of claim 12, wherein each said voltage surge suppressor is comprised exclusively of a varistor. 
     
     
       14. The fail-safe lightning arrestor apparatus of claim 13, wherein said varistors are metal oxide varistors. 
     
     
       15. The fail-safe lightning arrestor apparatus of claim 12, wherein said circuit breaker of each said combination circuit breaker-lightning arrestor is operative to afford overcurrent protection to a branch circuit wired between said load terminal thereof and the panelboard grounded neutral bus. 
     
     
       16. The fail-safe lightning arrestor apparatus defined in claim 15, wherein said trip unit of each said combination circuit breaker-lightning arrestor includes magnetically actuated trip elements operating to precipitate opening of the associated contacts in response to current of heavy overload and short circuit proportions drawn by either the associated suppressor or the associated branch circuit.